Exhaust aftertreatment systems are used to receive and treat exhaust gas generated by IC engines. Generally exhaust gas aftertreatment systems comprise any of several different components to reduce the levels of harmful exhaust emissions present in exhaust gas. For example, certain exhaust gas aftertreatment systems for diesel-powered IC engines comprise a selective catalytic reduction (SCR) system, including a catalyst formulated to convert NOx (NO and NO2 in some fraction) into harmless nitrogen gas (N2) and water vapor (H2O) in the presence of ammonia (NH3). Generally in such aftertreatment systems, an exhaust reductant (e.g., a diesel exhaust fluid such as urea) is injected into the SCR system to provide a source of ammonia and mixed with the exhaust gas to partially reduce the NOx gases. The reduction byproducts of the exhaust gas are then fluidly communicated to the catalyst included in the SCR system to decompose substantially all of the NOx gases into relatively harmless byproducts that are expelled out of the aftertreatment system.
Reductants used in SCR systems generally include a water based liquid such as, for example, an aqueous urea solution or a diesel exhaust fluid (DEF) as the source of ammonia. Such reductants have low ammonia content. For example, a commonly used reductant comprising aqueous urea solution includes 32.5w/w % urea to 67.5w/w % deionized water, but the ammonia content in the reductant is only about 18.5%. Other water based reductants are also prone to freezing at low temperatures, particularly at very low temperatures (e.g., below −11 degrees Celsius) or where the exhaust gas temperature is less than 170 degrees Celsius (e.g., on engine startup). Such reductants also cause reductant deposits to form in components of the aftertreatment system (e.g., in a reductant insertion assembly, hoses, tubes, or the SCR system) or any other surfaces in contact with the reductant. Reductant deposit formation is even higher at low temperatures. Furthermore, such reductants also have a high carbon footprint.